Since electronic device generates heat during operating, it will damage easily due to overheat without effective heat-dissipation. It is common to install a DC fan without bushing on electronic device for heat-dissipating. The DC fan without bushing has been well known to set various bearing like a ball bearing or an oily bearing between a fan wheel and a fan housing in order to enhance rotation and diminish noise of the fan. The oily bearing has porous structure made by sintering copper alloy or iron alloy so as to absorb a lubricant. However, the lubricant will be pushed to sputter by rotating a fan shaft to contaminate entire the fan housing when the fan shaft in the oily bearing rapidly rotates, and the oil-retaining quantity of the oily bearing decreases and distributes unevenly. Therefore, when the fan is used for a long time, the lubricating efficiency of bearing becomes bad gradually noise of bearing becomes loud gradually, even the fan will stop rotating.
A heat-dissipating fan was disclosed in R.O.C. Taiwan Patent No. 471557 entitled “ lubricating oil-circulating structure for fan shaft”, which is composed of a housing, a stator and a rotor. An oily bearing has a bearing body with through holes (i.e. axis holes). A ring portion is extended from one end of the bearing body to form an oil tank. A trench is set on the radial surface of bearing body to make a released lubricant flow to the trench by passing the through holes and return to the oil tank and the through holes by passing the trench. The oil tank is set at the ring portion of the oily bearing and the trench is set on the bearing body, so that the lubricant will flow to the end surface of the oily bearing to reduce oil-retaining quantity resulting in weakening lubricating effect. Besides, since the oil tank and the trench are the shape of a line easy to result in gathering lubricant at one side only, the oil-circulating efficiency of the lubricant becomes worse.